1. Technical Field
The present invention relates to a thin-film transistor forming substrate, a semiconductor device, and an electric apparatus.
2. Related Art
Recently, a general configuration of a flat panel display (FPD) such as a liquid crystal device, an organic EL display device, or an electrophoretic display device is disclosed in JP-A-2007-249231 and Japanese Patent No. 4366743. In the general configuration, an active matrix of TFTs is formed on a component substrate formed from a rigid glass substrate, and a flexible substrate (hereinafter, also referred to as an FPC) in which driving circuits are mounted is connected to the component substrate.
In a structure illustrated in FIG. 37A, three flexible substrates 601 in which a scanning line driving circuit 61, a data line driving circuit 62, and a common power source circuit 64 are mounted are connected to three sides of a component substrate 600, and it is common to use the flexible substrates 601 in a state of being folded to the rear face side of the component substrate 600. However, there are problems in that the thickness of the device is increased, and a frame area used for connections with the flexible substrates 601 is necessary. Generally, the width of the frame is in the range of about 3 to 5 mm.
In addition, in order to decrease the frame area, a configuration is practically employed in a liquid crystal device or the like in which built-in drivers are included. As shown in FIG. 37B, the scanning line driving circuit 61, the data line driving circuit 62, and the common power source circuit 64, which are used for driving a display unit 5, are formed on the surface of a substrate 600A configuring the component substrate 600 as built-in drivers. An external circuit substrate 202 used for driving the above-described built-in drivers is connected to one side of the substrate 600A through the flexible substrate 601.
Even in a case where low temperature polysilicon (LIPS) TFTs are used as TFTs configuring the built-in drivers, they are components having a mobility of 100 m2/V/sec. Thus, in order to bury the built-in drivers, a dead space of about several mm is necessary on each side of a display area.
In addition, as shown in FIGS. 37A and 37B, an external circuit substrate 202 is connected to at least one side of the substrate 600 through connection substrates 201 and 601, and the flexible substrates 601 are used in a state of being folded to the rear face side of the component substrate 600. Accordingly, as described above, this has an adverse effect on a decrease in the thickness, the weight, or the like of the device. Furthermore, since the external circuit substrate 202 is rigid, up to three sides of the FPD can be formed to be flexible. However, all four sides of the FPD cannot be formed to be flexible.
Although not yet implemented, a transfer process called a SUFTLA (Surface Free Technology by Laser Ablation) (registered trademark) or an EPLaR technique (Electronics on Plastic by Laser Release) has the following problems.
Currently, the flexible substrate is connected by being clamped to the component substrate such as a glass substrate that has high rigidity. When such mounting is performed for the component substrate having flexibility, a connection defect occurs immediately after the connection of the flexible substrate 601 or during use, so that a defect such as the formation of a short circuit or the like frequently occurs. Accordingly, there is a problem from the viewpoint of reliability.
In JP-A-2006-508406, although a substrate having flexibility in which an insulating polymer is used as the core is used as a metallic foil substrate, the above-described problems of the frame are not solved.
In addition, in JP-T-2004-518994 and Japanese Patent No. 3551194, although driving circuits are mounted on the surface of a component substrate, from the viewpoint of handling, there are practical problems such as the reliability of IC connection and the like. Although ICs are connected to the uppermost surface of the substrate, a thin-film organic EL is directly formed on the driving circuits, and accordingly, the reliability of the connection of the driving circuits is not enhanced. In addition, there is a problem from the viewpoint of robustness. Furthermore, in Japanese Patent No. 4189887, ICs are mounted on the rear face side of a substrate in an exposed state, or the ICs are covered with a rigid thermal diffuser, whereby there is a problem of flexibility.
As above, in order to realize a flexible display device, there is an object of devising a flexible substrate.